Active materials include those compositions that can exhibit a change in stiffness properties, shape and/or dimensions in response to an activation signal, which can be an electrical, magnetic, thermal or a like field depending on the different types of active materials. Preferred active materials include but are not limited to the class of shape memory materials, and combinations thereof. Shape memory materials, also sometimes referred to as smart materials, refer to materials or compositions that have the ability to “remember” their original shape, which can subsequently be “recalled” by applying an external stimulus (i.e., an activation signal). As such, deformation of the shape memory material from the original shape can be a temporary condition.
Shape memory materials such as shape memory alloys (SMAs) and polymers (SMPs) represent a class of thermally-activated smart materials (TASMs) that undergo a reversible phase transformation responsible for dramatic stress-induced and temperature-induced recoverable deformation behavior. SMAs and SMPs have been used for some years to produce novel and useful devices such as control actuators, deformable composite structures and various kinds of medical devices.